US2178046A - Drafting machine - Google Patents

Description

Oct. 31, 1939. c, H, LITTLE 2,178,046

DRAFTING MACHINE Original Filed Aug. 5, 1933 2 Sheets-Sheet 1 A TTORNEY5 Oct. 31, 1939. c. H. LITTLE DRAFTING MACHINE Original Filed Aug. 5, 1953 2 Sheets-Sheet 2 @fl {U i E6 N hk INVENTOR.

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A Mm g; mZf' ATTORN E Y5 UNITED STATES PATENT OFFiCE DRAFTING MACHINE Charles H. Little, Cleveland signer of one-tenth to Cleveland Heights,

Original application An 683,773. Divided and her 16, 1935, Serial N 0. 22, 1939 5 Claims.

The present invention relates to drafting machines of the parallel motion type, wherein an arm comprising a plurality of connected sections or parallelograms is employed to maintain par- 5 allelism of rulers and protractors as they are moved about a drawing board, and particularly to those drafting machines wherein the sections or parallelograms are of the wheel and band type.

The present application is a division of my copending application Serial No. 683,773, filed. August 5, 1933, entitled Drafting machine.

A very high degree of accuracy is required in machines of this character, and due to the particular construction thereof, slight errors or changes in the various parts, especially the parallelograms, result in multiplied errors at the rulers. Arms ofthe wheel and band type can be made to give very accurate parallelism to the 20 rulers but their use has been very limited because of the elasticity of the bands which results in instability or springiness at the ends of the rulers. The present invention overcomes this serious defeet without interfering with the free and easy movement of the arm, which is essential for both accuracy and convenience of operation.

Arms of the wheel and band type usually comprise two sections or parallelograms, each of which comprises a pair of equal diameter wheels rotatably connected to each other by either a single or double strut and carrying a taut band.

An object of the present invention is the provision of a band for a wheel and band type parallel motion mechanism-that will have a high resistance to tension, compared with its resistance to turning about the wheels, and also not require excessive tension to keep it taut. A number of means for obtaining this result will be herein described but the preferred construction consists of a single band of flexible material wrapped several times about the wheels with the ends and certain intermediate parts thereof clamped or fastened to the wheels. The band may be provided with transverse curvature, which construc- 5 tion reduces the amount of tension required to keep the same taut, and also tends to keep the several layers in alignment with each other.

Another object of the present invention is the provision of a novel drafting machine, comprising a wheel and band type arm in Which the band has a high resistance to tension, compared to its resistance to turning about the wheels.

Another object of the present invention is the provision of a novel drafting machine of the parallel motion type in which the protractor and Heights, Ohio, as- Charles Hubbard Little,

Ohio

gust 5, 1933, Serial No. this application Novem- 50,215. Renewed March handle lie much closer to the drawing board than the protractor and handle of machines of the prior art.

Another object of the present invention is the provision of a novel drafting machine of the parallel motion type comprising a wheel and band type of arm in which the center of the protractor is external of the band.

Further objects and advantages of the invention will be apparent to those skilled in the art from the following description of the preferred embodiments thereof described with reference to the accompanying drawings, in which Fig. 1 is a plan of a drafting machine embodying the present invention, attached to a drawing board;

Fig. 2 is a side elevation of the drafting machine and drawing board shown in Fig. 1;

Fig. 3 is a section on the line 33 of Fig 1, with portions in elevation;

Fig. 4 is a section on the line 4-4 of Fig. 3, with portions in elevation;

Fig. 5 is a plan of the band shown in Figs. 1 to 7 inclusive;

Fig. 6 is an enlargement of a portion of Fig. 1;

Fig. '7 is a section on the line 'i'l of Figs. 1, 2 and 6; v

Fig. 8 is a section similar to Fig. '7 illustrating a modified construction of band; and

Fig. 9 is a section similar to Figs. 7 and 8 illustrating a further modified construction of band.

Similar reference characters designate corresponding parts throughout the several figures. of the drawings.

Referring to the drawings, the drawing boards to which the several drafting machines are shown attached are designated by the reference character B. The drafting machine illustrated in Figs. 1 to 7 inclusive consists of a protractor A carried at one end of an arm C, the other end of which is pivotally attached to an anchor D. 'The anchor D is of well known construction, and per se forms no part of the present invention and will not be described in detail, sufifice it to say that the same is slidably supported on and adjustable along a bar I!) attached to the underside of the board B by brackets H.

The anchor parallelogram comprises two wheels l3 and M of equal diameter. The upper wheel [3 is fixed to a member l5 pivotally connected to the anchor D in a manner well known in the art, and the lower wheel i4 is connected to a tubular shaft I6, by means of anti-friction bearings l'!. The wheels [3 and M are spaced apart by means of an adjustable strut l9 provided with forked end members 20 and 2|. The upper end member 26 projects to either side of the wheel I3 and is rotatably connected thereto by means of anti-friction bearings in such a manner that it is free to oscillate about the center thereof as an axis. The lower forked end member 2| is connected to the tubular shaft l6 upon which the wheel I4 is rotatably supported. The wheels Hi and M are joined by a flexible band 25 in such a manner that the wheel I4 does not rotate with reference to the drawing board B and the wheel |3, as the strut I9 is 05- cillated about its pivoted connection. The band 25 runs between flanges on the periphery of the wheels i3 and H! which assist in retaining the band in position on the wheels, and is connected to each wheel in a manner hereinafter referred to.

The protractor parallelogram comprises two wheels 30 and 3| of equal diameter and similar in construction to the wheels 23 and M of the anchor parallelogram. The left-hand wheel 30 is rotatably connected to a tubular shaft 29 by anti-friction bearings 32, and the right-hand wheel 3| is pivotally supported by antifriction bearings, in a forked end member 33 of an adjustable strut 3Q similar in construction to the strut l9 previously referred to. The other extremity of the strut 3 1 is provided with a forked end member 35 which extends on either side of the wheel 33 and is connected to the tubular shaft 29 in such a manner that the strut 34 is free to oscillate about the axis of the wheel 30.

The wheels 36 and 3| are joined by a flexible band 38, similar to the band 25, in such a manner that the wheel 3| does not rotate with reference to the drawing board B and the wheel 361, as the strut 34 is oscillated about its pivoted connection with the tubular shaft 29. The flexible bands 25 and 38 each comprise a single strip of thin flexible material, preferably steel, wrapped about the wheels l3 and i i, and and 3|, respectively, a plurality of times. As illustrated, see Figs. 3 and 4, the strips are wrapped about their respective wheels four times. Both ends of the strip which forms the band 38 are attached to the wheel 30 by means of a screw 30 which extends through elongated slots ii formed in the strip, and the wheel 3| is attached to the band 38 in a similar manner by a screw, not shown, which projects through the elongated slots 42. The strip which forms the band 25 is attached to the wheels K: and H! in a similar manner.

The struts |9 and. 3 are adjustable for the purpose of assembling the bands on the wheels, and for taking up slack and producing tension in the band. In the embodiment of the invention illustrated, the construction of both struts is the same and the adjustment is accomplished by turning a tubular member 53, see Fig. l, threaded into the interior of the tubular strut member. A head 44 on the member 43 abuts against the adjacent forked end member which is prevented from turning with reference to the strut by a pin 45. The pin 45 is secured in the tubular strut member and projects through a slot 58 in a short shaft 41 fixed to the forked end member. The tubular member 33 is provided with a knurled hand grasp 48 for easy operation thereof, so constructed that it entirely conceals the thread in all working positions. The bands are adjusted to obtain the proper distribution of tension between the different layers by loosening the screws which attach the same to the wheels, and alternately applying and releasing the tension thereof and oscillating the sections or parallelograms. The elongated slots in the strips through which the screws pass permit the different layers of the band to adjust themselves after which the screws are tightened and the band held securely to the wheels independent of the friction between the band and the wheels. Clips 49 are preferably employed to keep the different layers of the band in alignment, especially where a perfectly flat band is employed, but these clips may be omitted if desired. The clips 49 permit longitudinal movement of the bands relative to each other, and may be held from longitudinal movement along the bands in any convenient manner.

It has been found that one-piece flexible bands wrapped about the wheels a number of times produce a very practical, cheap, and simple band which gives a high degree of stability at the outer end of the scales without adversely effecting the ease of motion of the arm. Multiple bands greatly increase the stability or lack of springiness at the outer end of the rulers by permitting a sufficiently large section to be employed to prevent undue stretch between the wheels without materially increasing the turning resistance when the band wraps and unwraps about the wheels, because the moment of resistance varies as the square of the layer thickness. This construction also reduces the amount of tension required to keep the bands taut and in turn the stresses in the parts between the wheels and the load on the bearings, etc. Attaching the bands to the wheels by means of the screws 40 also reduces these stresses by doing away with the necessity of sufflcient friction to prevent the wheels from turning in the bands. The tension in the bands and the stress in the struts often exceeds 200 pounds, and any reduction in the stresses to which the various parts are subjected results in easier turning.

The wheels I4 and 30 are connected together by screws 58 in such a manner that they move as a unit. The position of the screw 50 is limited by the extreme positions of the struts I9 and 34, shown in dotted lines in Fig. 4, as they oscillate a maximum of approximately A spacer collar 5| is employed to keep the wheels in proper spaced relationship.

A member 55 secured to the underside of the wheel 3| carries the protractor assembly A detachably secured thereto by screws 56. The protractor assembly is of well known construction and per se does not form a part of the present invention and will not be described in detail, suffice it to say that it comprises the protractor proper designated by the reference character 51, a handle 58, and the rulers 59 and 5D. The center of the protractor is located externally of the band 38 which construction permits the handle 58 and the band to lie much closer to the drawing and avoids any interference of the hand of the operator with the band or wheel. This construction is also advantageous when working at the left hand part of the drawing, especially in angular positions, as it places the rules further from the bands.

Figs. 8 and 9 show transversely curved bands. The bands shown in these figures are similar to the bands 25 and 38 shown in Figs. 1 to 7 inclusive, except for the fact that they are transversely curved. In Fig. 9 one of the layers of the band 64 is shown curved in a reverse direction. Transversely curving the bands as illustrated in Figs. 8 and 9 assists in keeping the various layers in alignment and reduces the amount of tension necessary to keep the bands taut. In some light, small machines, particularly when the transverse curved bands are employed, pin bearings may be used in place of the ball bearings illustrated, thus simplifying the construction and lowering the cost of the machine.

The preferred embodiment of the present invention has been illustrated and described, but I do not wish to be limited to the particular construction shown, which may be varied within the scope of this invention. The present applica tion is intended to cover all adaptations, variations and modifications of the construction shown which come Within the customary practices of those skilled in the art to which the invention relates. I particularly point out and claim as my invention the following:

I claim:

1. In a drafting machine the combination of a parallel motion arm, an anchor at one end of said arm for operatively connecting the same to a drawing board or the like, a protractor assembly at the other end of said arm, said arm com,- prising a pair of wheels, and a ribbon-like laminated band operatively connecting said wheels and comprising a continuous band encircling said Wheels a plurality of times.

2. In a drafting machine the combination of a parallel motion arm, an anchor at one end of said arm for operatively connecting the same to a drawing board or the like, a protractor assembly at the other end of said arm, said arm comprising a pair of wheels, a ribbon-like laminated band encircling said Wheels and comprising a continuous band encircling said wheels a plurality of times, and means for attaching said band to said wheels independent of the friction therebetween.

3. In a drafting machine the combination of a parallel motion arm, an anchor at one end of said arm for a drawing board or the like, a protractor assembly at the other end of said arm, said arm comprising a pair of wheels, a laminated band encircling said wheels, and members carried by said band intermediate said wheels for maintaining the layers of said band in alignment.

4. In a drafting machine the combination of a parallel motion arm, an anchor at one end of said arm for operatively connecting the same to a drawing board or the like, a protractor assembly at the other end of said arm, said arm comprising a pair of wheels, and a transversely curved band operatively connecting said Wheels.

5. In a drafting machine the combination of a parallel motion arm, an anchor at one end of said arm for operatively connecting the same to a drawing board or the like, a protractor assembly at'the other end of said arm, said arm comprising a pair of Wheels, and a transversely curved laminated band encircling said wheels.

CHARLES H. LITTLE.

operatively connecting the same to

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